1. Field of the Invention
This Invention relates to a film image reading system for reproducing the image recorded on the original sheet film, and more particularly to the adjustment of density at the time of the reading of the image on the original sheet film, by reading the projected image obtained by projecting the image of the original sheet film on the main unit of the film image reading system by means of a film projector.
2. Prior Art
In order to reproduce the images recorded on 35 mm film or the like in the form of prints in a desired size, it is in general practice to obtain prints of such images by printing the images on photosensitive paper. However, this process of printing such images on sensitive paper requires highly specialized techniques as well as special equipment and facilities. Thus, it has hitherto been impossible for laymen to perform such printing work in any easy and convenient way. In addition, the price for such prints are fairly high, and consequently it has not been free from care to have film images reproduced on such prints in a desired size.
In the meanwhile, the progress attained in the color copying machines in the recent years has made it possible to reproduce the images recorded on paper with a high degree of precision by the color copying process. On top of this, various types of image processing techniques made possible by processing such images in the form of digital signals, such as the technique offering the enlarging and reducing functions, have attained considerable progress in the development of multifarious functions, with such features as the enhanced color reproducing capability, the improved reproducing the details with high precision and fineness, and the image synthesizing process, in color copying machines.
In view of these circumstances, it has been proposed to perform the color copying process with a proper copying machine on the basis of the image signals obtained by projecting by means of a film projector the images recorded on various types of film and by obtaining electrical image signals by reading the said projected images with an image reading system equipped with a photoelectric conversion element, such as a CCD sensor provided in a digital color copying machine. Moreover, it has been in practice to install a film projector on a hitherto available analog copying machine and to copy the film images as projected by such a film projector or to print such images by applying such projected images directly to the photosensitive material.
In this regard, the density range of the film for recording images thereon generally presents a wide range of difference, and, in addition, this factor, density range, is different from one type of film to another, such as negative film and reversal film. For instance, the density range on negative film is ordinarily about 2 at most while that on reversal film is about 3 or more, and, above all, the density range on reversal film is wider than that of the other. Additionally, even the same type of film presents differences in the distribution of the density range, depending on the differences among the film manufacturers.
On the other hand, the reading range of the image input terminal (IIT) in the image reading system of the color copying machine is approximately 1.8 but, with an IIT having such a reading range like this, it is not possible to read the images with accuracy over the entire density range on negative film and reversal film.
Therefore, it has been a prior approach to the solution of this problem to change the amount of light from the light source lamp of the projector and to read only the effectively used density range out of a wider density range by varying the amount of light emitted from the light source lamp of the film projector.
For the light source lamp of a film projector intended for an applications like this, a halogen lamp is commonly used, but, in case this halogen lamp is employed for the projection of film, the lamp gives influence on the ratios of the red (R), green (G), and blue (B) carried on the projected light in consequence of the spectroscopic characteristics of the lamp, so that the reproduced image assumes a bluish tint or a reddish tint, as the case may be, because a halogen lamp generally has such spectroscopic characteristics that the light emitted therefrom contains a more considerable amount of red (R) but a lesser amount of blue (B). Therefore, it cannot be considered sufficient merely to change the amount of light from such a lamp if it is to be made possible for the image reading system accurately to read the images from the film.
Moreover, this state is not limited to a halogen lamp. Even when any other type of lamp other is to be used, the process of varying the amount of light emitted from the lamp is not capable of making separate adjustments of the density for R, G, and B in order to correct the deterioration of color balance resulting from such factors as the condition of illumination at the time of film shooting and the condition of development applied to the film.
Thus, it is not possible to obtain a copy giving an impression favorable to sight when a film image is copied merely with a process for varying the amount of light from the lamp.